Switch to on-by-default XSS escaping for rails.

  This consists of:

  * String#html_safe! a method to mark a string as 'safe'
  * ActionView::SafeBuffer a string subclass which escapes anything unsafe which is concatenated to it
  * Calls to String#html_safe! throughout the rails helpers
  * a 'raw' helper which lets you concatenate trusted HTML from non-safety-aware sources (e.g. presantized strings in the DB)
  * New ERB implementation based on erubis which uses a SafeBuffer instead of a String

Hat tip to Django for the inspiration.

19 files changed, 112 insertions, 32 deletions

diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 664cc3b562..5a4e1bee43 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -260,7 +260,7 @@ module ActionView #:nodoc:
       @assigns = assigns_for_first_render.each { |key, value| instance_variable_set("@#{key}", value) }
       @controller = controller
       @helpers = self.class.helpers || Module.new
-      @_content_for = Hash.new {|h,k| h[k] = "" }
+      @_content_for = Hash.new {|h,k| h[k] = ActionView::SafeBuffer.new }
       self.view_paths = view_paths
     end
 
diff --git a/actionpack/lib/action_view/erb/util.rb b/actionpack/lib/action_view/erb/util.rb
index 3c77c5ce76..f767a5e27e 100644
--- a/actionpack/lib/action_view/erb/util.rb
+++ b/actionpack/lib/action_view/erb/util.rb
@@ -15,9 +15,19 @@ class ERB
     #   puts html_escape("is a > 0 & a < 10?")
     #   # => is a &gt; 0 &amp; a &lt; 10?
     def html_escape(s)
-      s.to_s.gsub(/[&"><]/) { |special| HTML_ESCAPE[special] }
+      s = s.to_s
+      if s.html_safe?
+        s
+      else
+        s.gsub(/[&"><]/) { |special| HTML_ESCAPE[special] }.html_safe!
+      end
     end
 
+    alias h html_escape
+
+    module_function :html_escape
+    module_function :h
+
     # A utility method for escaping HTML entities in JSON strings.
     # This method is also aliased as <tt>j</tt>.
     #
diff --git a/actionpack/lib/action_view/helpers.rb b/actionpack/lib/action_view/helpers.rb
index 652561f7f8..d63e8602f1 100644
--- a/actionpack/lib/action_view/helpers.rb
+++ b/actionpack/lib/action_view/helpers.rb
@@ -15,6 +15,7 @@ module ActionView #:nodoc:
     autoload :JavaScriptHelper, 'action_view/helpers/javascript_helper'
     autoload :NumberHelper, 'action_view/helpers/number_helper'
     autoload :PrototypeHelper, 'action_view/helpers/prototype_helper'
+    autoload :RawOutputHelper, 'action_view/helpers/raw_output_helper'
     autoload :RecordIdentificationHelper, 'action_view/helpers/record_identification_helper'
     autoload :RecordTagHelper, 'action_view/helpers/record_tag_helper'
     autoload :SanitizeHelper, 'action_view/helpers/sanitize_helper'
@@ -46,6 +47,7 @@ module ActionView #:nodoc:
     include JavaScriptHelper
     include NumberHelper
     include PrototypeHelper
+    include RawOutputHelper
     include RecordIdentificationHelper
     include RecordTagHelper
     include SanitizeHelper
diff --git a/actionpack/lib/action_view/helpers/active_model_helper.rb b/actionpack/lib/action_view/helpers/active_model_helper.rb
index 3e6e62237d..c9231225e1 100644
--- a/actionpack/lib/action_view/helpers/active_model_helper.rb
+++ b/actionpack/lib/action_view/helpers/active_model_helper.rb
@@ -91,6 +91,7 @@ module ActionView
         yield contents if block_given?
         contents << submit_tag(submit_value)
         contents << '</form>'
+        contents.html_safe!
       end
 
       # Returns a string containing the error message attached to the +method+ on the +object+ if one exists.
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index 95f00cda39..faa7f2e2e9 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -289,7 +289,7 @@ module ActionView
         else
           sources = expand_javascript_sources(sources, recursive)
           ensure_javascript_sources!(sources) if cache
-          sources.collect { |source| javascript_src_tag(source, options) }.join("\n")
+          sources.collect { |source| javascript_src_tag(source, options) }.join("\n").html_safe!
         end
       end
 
@@ -440,7 +440,7 @@ module ActionView
         else
           sources = expand_stylesheet_sources(sources, recursive)
           ensure_stylesheet_sources!(sources) if cache
-          sources.collect { |source| stylesheet_tag(source, options) }.join("\n")
+          sources.collect { |source| stylesheet_tag(source, options) }.join("\n").html_safe!
         end
       end
 
@@ -584,7 +584,7 @@ module ActionView
 
         if sources.is_a?(Array)
           content_tag("video", options) do
-            sources.map { |source| tag("source", :src => source) }.join
+            sources.map { |source| tag("source", :src => source) }.join.html_safe!
           end
         else
           options[:src] = path_to_video(sources)
diff --git a/actionpack/lib/action_view/helpers/capture_helper.rb b/actionpack/lib/action_view/helpers/capture_helper.rb
index c90acc5ac2..b62df75dbb 100644
--- a/actionpack/lib/action_view/helpers/capture_helper.rb
+++ b/actionpack/lib/action_view/helpers/capture_helper.rb
@@ -143,7 +143,7 @@ module ActionView
       # Defaults to a new empty string.
       def with_output_buffer(buf = nil) #:nodoc:
         unless buf
-          buf = ''
+          buf = ActionView::SafeBuffer.new
           buf.force_encoding(output_buffer.encoding) if buf.respond_to?(:force_encoding)
         end
         self.output_buffer, old_buffer = buf, output_buffer
diff --git a/actionpack/lib/action_view/helpers/date_helper.rb b/actionpack/lib/action_view/helpers/date_helper.rb
index 8a7a870b99..4b51dc7856 100644
--- a/actionpack/lib/action_view/helpers/date_helper.rb
+++ b/actionpack/lib/action_view/helpers/date_helper.rb
@@ -916,15 +916,15 @@ module ActionView
 
     class InstanceTag #:nodoc:
       def to_date_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_date
+        datetime_selector(options, html_options).select_date.html_safe!
       end
 
       def to_time_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_time
+        datetime_selector(options, html_options).select_time.html_safe!
       end
 
       def to_datetime_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_datetime
+        datetime_selector(options, html_options).select_datetime.html_safe!
       end
 
       private
diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index 32b9c4a7dd..c46b39fc23 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -282,7 +282,7 @@ module ActionView
 
         concat(form_tag(options.delete(:url) || {}, options.delete(:html) || {}))
         fields_for(object_name, *(args << options), &proc)
-        concat('</form>')
+        concat('</form>'.html_safe!)
       end
 
       def apply_form_for_options!(object_or_array, options) #:nodoc:
@@ -809,7 +809,7 @@ module ActionView
         add_default_name_and_id(options)
         hidden = tag("input", "name" => options["name"], "type" => "hidden", "value" => options['disabled'] && checked ? checked_value : unchecked_value)
         checkbox = tag("input", options)
-        hidden + checkbox
+        (hidden + checkbox).html_safe!
       end
 
       def to_boolean_select_tag(options = {})
diff --git a/actionpack/lib/action_view/helpers/form_options_helper.rb b/actionpack/lib/action_view/helpers/form_options_helper.rb
index 3db5202e7d..935ab5f3e8 100644
--- a/actionpack/lib/action_view/helpers/form_options_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_options_helper.rb
@@ -296,7 +296,7 @@ module ActionView
           options << %(<option value="#{html_escape(value.to_s)}"#{selected_attribute}#{disabled_attribute}>#{html_escape(text.to_s)}</option>)
         end
 
-        options_for_select.join("\n")
+        options_for_select.join("\n").html_safe!
       end
 
       # Returns a string of option tags that have been compiled by iterating over the +collection+ and assigning the
diff --git a/actionpack/lib/action_view/helpers/form_tag_helper.rb b/actionpack/lib/action_view/helpers/form_tag_helper.rb
index 1d851ecbd7..7688e786b1 100644
--- a/actionpack/lib/action_view/helpers/form_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_tag_helper.rb
@@ -440,7 +440,7 @@ module ActionView
         concat(tag(:fieldset, options, true))
         concat(content_tag(:legend, legend)) unless legend.blank?
         concat(content)
-        concat("</fieldset>")
+        concat("</fieldset>".html_safe!)
       end
 
       private
@@ -467,14 +467,14 @@ module ActionView
 
         def form_tag_html(html_options)
           extra_tags = extra_tags_for_form(html_options)
-          tag(:form, html_options, true) + extra_tags
+          (tag(:form, html_options, true) + extra_tags).html_safe!
         end
 
         def form_tag_in_block(html_options, &block)
           content = capture(&block)
           concat(form_tag_html(html_options))
           concat(content)
-          concat("</form>")
+          concat("</form>".html_safe!)
         end
 
         def token_tag
diff --git a/actionpack/lib/action_view/helpers/prototype_helper.rb b/actionpack/lib/action_view/helpers/prototype_helper.rb
index 03f1dabb4e..8c1f0ad81f 100644
--- a/actionpack/lib/action_view/helpers/prototype_helper.rb
+++ b/actionpack/lib/action_view/helpers/prototype_helper.rb
@@ -395,7 +395,7 @@ module ActionView
 
         concat(form_remote_tag(options))
         fields_for(object_name, *(args << options), &proc)
-        concat('</form>')
+        concat('</form>'.html_safe!)
       end
       alias_method :form_remote_for, :remote_form_for
 
diff --git a/actionpack/lib/action_view/helpers/raw_output_helper.rb b/actionpack/lib/action_view/helpers/raw_output_helper.rb
new file mode 100644
index 0000000000..79b0e4ee75
--- /dev/null
+++ b/actionpack/lib/action_view/helpers/raw_output_helper.rb
@@ -0,0 +1,9 @@
+module ActionView #:nodoc:
+  module Helpers #:nodoc:
+    module RawOutputHelper
+      def raw(stringish)
+        stringish.to_s.html_safe!
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/actionpack/lib/action_view/helpers/sanitize_helper.rb b/actionpack/lib/action_view/helpers/sanitize_helper.rb
index d89b955317..69d0d0fb67 100644
--- a/actionpack/lib/action_view/helpers/sanitize_helper.rb
+++ b/actionpack/lib/action_view/helpers/sanitize_helper.rb
@@ -49,7 +49,11 @@ module ActionView
       # confuse browsers.
       #
       def sanitize(html, options = {})
-        self.class.white_list_sanitizer.sanitize(html, options)
+        returning self.class.white_list_sanitizer.sanitize(html, options) do |sanitized|
+          if sanitized
+            sanitized.html_safe!
+          end
+        end
       end
 
       # Sanitizes a block of CSS code. Used by +sanitize+ when it comes across a style attribute.
@@ -72,7 +76,11 @@ module ActionView
       #   strip_tags("<div id='top-bar'>Welcome to my website!</div>")
       #   # => Welcome to my website!
       def strip_tags(html)
-        self.class.full_sanitizer.sanitize(html)
+        returning self.class.full_sanitizer.sanitize(html) do |sanitized|
+          if sanitized
+            sanitized.html_safe!
+          end
+        end
       end
 
       # Strips all link tags from +text+ leaving just the link text.
diff --git a/actionpack/lib/action_view/helpers/tag_helper.rb b/actionpack/lib/action_view/helpers/tag_helper.rb
index 7fae0f6b8d..ceddbd8cc1 100644
--- a/actionpack/lib/action_view/helpers/tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/tag_helper.rb
@@ -41,7 +41,7 @@ module ActionView
       #   tag("img", { :src => "open &amp; shut.png" }, false, false)
       #   # => <img src="open &amp; shut.png" />
       def tag(name, options = nil, open = false, escape = true)
-        "<#{name}#{tag_options(options, escape) if options}#{open ? ">" : " />"}"
+        "<#{name}#{tag_options(options, escape) if options}#{open ? ">" : " />"}".html_safe!
       end
 
       # Returns an HTML block tag of type +name+ surrounding the +content+. Add
@@ -94,7 +94,7 @@ module ActionView
       #   cdata_section(File.read("hello_world.txt"))
       #   # => <![CDATA[<hello from a text file]]>
       def cdata_section(content)
-        "<![CDATA[#{content}]]>"
+        "<![CDATA[#{content}]]>".html_safe!
       end
 
       # Returns an escaped version of +html+ without affecting existing escaped entities.
@@ -128,7 +128,7 @@ module ActionView
 
         def content_tag_string(name, content, options, escape = true)
           tag_options = tag_options(options, escape) if options
-          "<#{name}#{tag_options}>#{content}</#{name}>"
+          "<#{name}#{tag_options}>#{content}</#{name}>".html_safe!
         end
 
         def tag_options(options, escape = true)
@@ -143,7 +143,7 @@ module ActionView
                 attrs << %(#{key}="#{final_value}")
               end
             end
-            " #{attrs.sort * ' '}" unless attrs.empty?
+            " #{attrs.sort * ' '}".html_safe! unless attrs.empty?
           end
         end
     end
diff --git a/actionpack/lib/action_view/helpers/url_helper.rb b/actionpack/lib/action_view/helpers/url_helper.rb
index 204d4d71e1..e651bc17a9 100644
--- a/actionpack/lib/action_view/helpers/url_helper.rb
+++ b/actionpack/lib/action_view/helpers/url_helper.rb
@@ -93,7 +93,7 @@ module ActionView
           polymorphic_path(options)
         end
 
-        escape ? escape_once(url) : url
+        (escape ? escape_once(url) : url).html_safe!
       end
 
       # Creates a link tag of the given +name+ using a URL created by the set
@@ -220,7 +220,7 @@ module ActionView
         if block_given?
           options      = args.first || {}
           html_options = args.second
-          concat(link_to(capture(&block), options, html_options))
+          concat(link_to(capture(&block), options, html_options).html_safe!)
         else
           name         = args[0]
           options      = args[1] || {}
@@ -238,7 +238,7 @@ module ActionView
           end
 
           href_attr = "href=\"#{url}\"" unless href
-          "<a #{href_attr}#{tag_options}>#{name || url}</a>"
+          "<a #{href_attr}#{tag_options}>#{ERB::Util.h(name || url)}</a>".html_safe!
         end
       end
 
@@ -309,8 +309,8 @@ module ActionView
 
         html_options.merge!("type" => "submit", "value" => name)
 
-        "<form method=\"#{form_method}\" action=\"#{escape_once url}\" class=\"button-to\"><div>" +
-          method_tag + tag("input", html_options) + request_token_tag + "</div></form>"
+        ("<form method=\"#{form_method}\" action=\"#{escape_once url}\" class=\"button-to\"><div>" +
+          method_tag + tag("input", html_options) + request_token_tag + "</div></form>").html_safe!
       end
 
 
diff --git a/actionpack/lib/action_view/render/partials.rb b/actionpack/lib/action_view/render/partials.rb
index 7f10f54d2e..4f60566a09 100644
--- a/actionpack/lib/action_view/render/partials.rb
+++ b/actionpack/lib/action_view/render/partials.rb
@@ -223,7 +223,7 @@ module ActionView
         end
 
         result = template ? collection_with_template(template) : collection_without_template
-        result.join(spacer)
+        result.join(spacer).html_safe!
       end
 
       def collection_with_template(template)
diff --git a/actionpack/lib/action_view/safe_buffer.rb b/actionpack/lib/action_view/safe_buffer.rb
new file mode 100644
index 0000000000..8ba9cd80d6
--- /dev/null
+++ b/actionpack/lib/action_view/safe_buffer.rb
@@ -0,0 +1,28 @@
+
+module ActionView #:nodoc:
+  class SafeBuffer < String
+    def <<(value)
+      if value.html_safe?
+        super(value)
+      else
+        super(CGI.escapeHTML(value))
+      end
+    end
+
+    def concat(value)
+      self << value
+    end
+
+    def html_safe?
+      true
+    end
+
+    def html_safe!
+      self
+    end
+
+    def to_s
+      self
+    end
+  end
+end
\ No newline at end of file
diff --git a/actionpack/lib/action_view/template/handlers/erb.rb b/actionpack/lib/action_view/template/handlers/erb.rb
index aab7baf442..a780ab8d85 100644
--- a/actionpack/lib/action_view/template/handlers/erb.rb
+++ b/actionpack/lib/action_view/template/handlers/erb.rb
@@ -1,7 +1,31 @@
 require 'active_support/core_ext/class/attribute_accessors'
+require 'active_support/core_ext/string/output_safety'
+require 'erubis'
 
 module ActionView
   module TemplateHandlers
+    class Erubis < ::Erubis::Eruby
+      def add_preamble(src)
+        src << "@output_buffer = ActionView::SafeBuffer.new;"
+      end
+
+      def add_text(src, text)
+        src << "@output_buffer << ('" << escape_text(text) << "'.html_safe!);"
+      end
+
+      def add_expr_literal(src, code)
+        src << '@output_buffer << ((' << code << ').to_s);'
+      end
+
+      def add_expr_escaped(src, code)
+        src << '@output_buffer << ' << escaped_expr(code) << ';'
+      end
+
+      def add_postamble(src)
+        src << '@output_buffer.to_s'
+      end
+    end
+
     class ERB < TemplateHandler
       include Compilable
 
@@ -15,11 +39,9 @@ module ActionView
       self.default_format = Mime::HTML
 
       def compile(template)
-        require 'erb'
-
         magic = $1 if template.source =~ /\A(<%#.*coding[:=]\s*(\S+)\s*-?%>)/
         erb = "#{magic}<% __in_erb_template=true %>#{template.source}"
-        ::ERB.new(erb, nil, erb_trim_mode, '@output_buffer').src
+        Erubis.new(erb, :trim=>(self.class.erb_trim_mode == "-")).src
       end
     end
   end
diff --git a/actionpack/lib/action_view/test_case.rb b/actionpack/lib/action_view/test_case.rb
index 441f462bc9..8beda24aba 100644
--- a/actionpack/lib/action_view/test_case.rb
+++ b/actionpack/lib/action_view/test_case.rb
@@ -55,7 +55,7 @@ module ActionView
     setup :setup_with_controller
     def setup_with_controller
       @controller = TestController.new
-      @output_buffer = ''
+      @output_buffer = ActionView::SafeBuffer.new
       @rendered = ''
 
       self.class.send(:include_helper_modules!)